T cells can survive hematopoietic stem/progenitor cell transplants (HSPCT) following non-ablative and ablative conditioning regimens, for example radioresistant T cells mediate resistance to hematopoietic grafts and infection. Recent findings suggest that memory T cells (TM) should survive more effectively vs. naive cells as a result of enhanced anti-apoptotic regulation in this subset and new preliminary findings in this proposal demonstrate survival and expansion of infused and endogenous antigen specific host TM post- transplant. The experiments in this project will address questions testing the hypothesis that existing CDS TM pre-conditioning and TM infused at the time of transplant will result in enhanced antigen-specific immunity in the early (reconstituting) post-transplant immune compartment Experiments will examine the survival, expansion and function of memory populations and compare them to naive T cells in the post-HSPCT recipient. To accomplish these studies we will utilize and compare TCR transgenic (OT-I) and non-transgenic (H60) antigen specific TM including in vitro derived memory populations. Experiments in aim I are directed to elucidating the transplant parameters including conditioning and T cell replete or depleted inoculum on host memory cell survival in models designed to track these TM populations. The involvement of IL-15 and IL-7 in the maintenance and expansion of TM will be examined using fusion proteins and knock-out strains and experiments will also examine the role of CD30-CD30L interaction by memory cells post-transplant. Studies in aim II will examine the capacity of memory cells present to be reactivated in the reconstituting host's lymphoid compartment. Antigen delivery will be examined using syngeneic host APC and compared to syngeneic tumors transfected with surrogate antigen. The effectiveness of gp96-lg transfectants as an antigen delivery vehicle will be investigated as well as IL-15 transfected tumor populations. Functional evaluation of responses by reactivated TM will be carried out using immune analyses. Finally, studies in aim III are designed to examine the ability of memory populations to respond to tumor antigens post-HSPCT. Models will be examined in which recipients bearing tumors will be administered vaccines in attempts to augment anti-tumor responses in the early post-transplant period.